You can always benefit from the three points discussed in the following section to improve the sync and activity for Airmail.

Generally, the background activity for Airmail depends on this question, "How many apps are youusing in background?" Therefore, if you limit the number of background apps, Airmail will get more priority for the background sync. This will also get Airmail to download the message bodies quickly.

Secondly, if you use Airmail regularly throughout the day, it will get priority to sync in background,quickly.

And last, but equally important is to keep the Airmail app in the dock of your iOS device.This will prioritise Airmail's activity.